1. Field of the Invention
The present invention relates to a focus detection system for use in a camera, and more particularly to a focus detection system which can detect a focus in a far-near competition state which is caused by a plurality of objects of different object distances in a detection view field.
2. Description of the Prior Art
A focus detection system for a camera which detects a focus of an imaging lens by detecting a deviation between two images formed by dividing a pupil of the imaging lens of the camera is disclosed in U.S. Pat. No. 4,185,191 and Japanese Patent Application Laid-Open Nos. 118019/1980 and 155331/1980. In those systems, the two images formed are imaged on a sensor to photo-electrically convert the image information. The photo-electrically converted signals or the two images are processed to detect focus. The signal processing method is disclosed, for example, in U.S. Pat. No. 4,333,007. The signal processing method by the disclosed method is a excellent method for detecting a deviation from an in-focus position of a single image, but if a plurality of objects having different object distances are in a view field or if an object has a substantial three-dimensional spread, focus is set to a middle point of the plurality of objects in spite of the detection of the in-focus state by a calculation formula used in the processing and the focus is not set to a desired object. In the present specification, such a state of the objects is called "far-near competition".
A method which aims to resolve the problem of far-near competition is shown in Japanese Patent Application Laid-Open No. 75607/1981. However, this method does not completely resolve the problem of far-near competition.
A signal processing method used for detecting a focus is also shown in Japanese Patent Application No. 142306/1983 by the same inventor as that of the present invention. In this method, a drive distance (defocus distance) of a lens is determined based on a sum of minimum or maximum photo-electrically converted outputs of pixels corresponding to each other in a sensor for sensing the two images. However, this method also does not resolve the problem of far-near competition.